[unreadable] Tendon and ligament tears present a major clinical problem in orthopedic surgery, resulting in morbidity and function loss to the inflicted patients. The repair of torn tendons encounters major difficulties, and often results in impaired healing and function loss. Tissue engineering, which aims to construct three-dimensional tissues available as a source for implantation and tissue replacement is a novel approach in regenerative medicine. We have been studying novel biomaterials and ex vivo culture systems for ligament tissue engineering, while the Israeli PI has identified a novel pathway in mesenchymal stem cell (MSCs) differentiation to ligament/ tendon tissues mediated jointly by SMAD8 and BMP2 genes. Thus, in the present application we propose to promote tendon tissue formation by combining the two strategies: MSCs expressing novel signaling molecules and designated scaffolds. We therefore hypothesize that in vivo tendon repair could be achieved by combining specially designed silk scaffolds with mesenchymal stem cells co-expressing SMAD8 and BMP2 genes. In order to explore our hypothesis the following specific aims will be pursued: Specific Aim 1: In vitro culture of MSCs over expressing SMAD8/BMP2 genes on silk scaffolds. Genetically engineered MSCs will be cultured on silk scaffolds in vitro. Differentiation will be monitored and characterized on various hierarchical scales (gene/protein expression and structure). Specific Aim 2: Functional evaluation of engineered tendons in vivo. Engineered tendons will be tested in vivo to evaluate their phenotype stability, and the capacity to function and remodel under the conditions of physiological loading. Silk scaffolds seeded with genetically engineered and non-engineered MSCs will be implanted ectopically and in a tendon injury site. Tendon tissue engraftment, survival and regeneration will be evaluated. [unreadable] Finally we believe that our platform for generating tendon tissues applying novel signaling pathway represents a powerful system for producing a functional biological tendon substitute. In addition, our approach should pave the way for novel modalities in designing biological grafts available for implantation worldwide. [unreadable] This research will be done primarily in Israel at the Hebrew University of Jerusalem in collaboration with Gazit Dan as an extension of another NIH grant. [unreadable] [unreadable]